Speaker



Sept. 17, 1929. FIT-CH 1,728,405

SPEAKER Filed Nov. 24, 1928 2 Sheets-Sheet 1 INVENTOR w'ro r e 2 Sheets-Sheet 2 c. J. FITCH SPEAKER Filed Nov. 24, 1928 INVENTOR gen! . O n 2 .r.- 9 J .4. 4 N z L w Sm N. m Nz MM 0 9 +22? 0 3 Z ,w 7 N v 1 3 to e Z 7 MW M 4 z w w Sept. 17, 1929.

Patented Sept. 1929 2 UNITED STATES PATENT OFFICE CLYDE J. FITCH, OF BROOKLYN, NEW YORK SPEAKER Special objects of this invention are to provide a particularly sensitive and at the same time powerful telephonic speaker, which will be of relatively simple, inexpensive and durable construction and which will reproduce the original sounds with fidelity throughout the range of audibility and free of any chattering or extraneous noises.

The invention involves various novel features of construction, combinations andrelations of parts as will be clear from thefollowing specification.

The drawings accompanying and forming part of this specification illustrate certain practical embodiments of the invention, but it is to be understood that the structure may be modified as regards this particular disclosure without departure from the true spirit and broad scope of the invention.

0 Fig. 1 is a side elevation of an embodiment of the speaker; Fig. 2 is an enlarged broken and part sectional view of the magnet and coil system of the apparatus; Fig. 3 is an end view of one of the bifurcated poles with the coils thereon Fig. 4 is a broken plan view of the device; Figs. 5 and 6 are front and side views respectively, the latter partially broken to show details of a laminated form of the polar construction; Fig. 7 is a diagrammatic view illustrating particularly how the same set of coils may be used as combination field. and armature coils. Fig. 8is a simplified form of diagram illustrating the bridge'connection of the actuating current on the polarizing coils.

In Fig. 1 an electro-ma et is shown made up of a back piece 7 and we side pieces 8, 9 secured together by throu h bolts 10, the back piece being surrounded b a magnetizing coil 11 and the through b ts supporting the structure on an upstanding bracket 12. The nuts 13 on said bolts rigidly fasten the magnet on this upright bracket which is shown. 1

as braced on the bottom by an angle bracket 14. The foot of this angle bracket and the angular base 15 of the upright bracket being secured by bolts 16 on a supporting base 17. An insulating plate 18 secured by nuts 19 on the rearward ends of the through bolts serves as a base for the binding posts 20 of the magnetizin coil.

Attached to t e yoke of the magnet are the ole pieces 21, 22 and these pole pieces are of ifurcated construction to provide spaced pole tips 23, 24 and 25, 26. On the legs of these pole pieces are the coils 27 28 and 29, 30. The two pairs of pole tips 23, 24 and 25, 26 respectively'are shown as cut off straight and spaced in parallel relation providing as indicated in Fig. 2 two laterally spaced magnetic gaps 31. Operating in these gaps is an armature 32 of magnetic material such as soft iron having parallel top and bottom sides opposed to and parallel with the four tips of the pole pieces, said armature being shown as of rectangular cross-section having a width about or slightly less than the space between likepoles of a pair and a thickness slightly less than the space between opposing pairs of pole tips and being supported with its corner edges substantially equi-distant from the four diagonally o posite corners of the spaced pole tips. e armature so constructed and supported is thus subject equally to the pull of all four pole tips and hence magnetically balanced in the gaps.

For supporting the armature centralized in a balanced state and guided for substantially straight line movement in the gaps, flatspring strips 33 are shown supported at top and bottom at 34in arallel relation at the outer sides of'the p0 e pieces, the armature being riveted, soldered or otherwise secured at its ends at 35 to the intermediate portions of these strips, which preferably are of nonmagnetic material. The supporting stri s 33 yield sufliciently to enable movement 0 the armature substantially in the plane of the double-ended arrow shown in Fig. 2, such movement being by or past the pole tips with substantially constant spacin between the armature and adjacent faces 0 the pole tips, irrespective of the amplitude of armature movement. Thus the armature may travel the maximum ofmovement permissible by the supportin strips without possibility of contact with t e ole tips. Y

A drive rod 36 1s shownattached to the central portion of the armature and as connected out from the ends of the side clamps.

with a sound generating cone 37. While a small cone, with this unit, serves for the reproduction of the bass as well as the treble tones, it will be understood that other forms of reproducing elements may be employed.

The speaker cciis 27, 28 and 29, 30' are connected so as to alternately aid oppose the magnetization of the poles 23, 24 and 25, 26. Thus in the illustration Fig. 2 where the upper poles are magnetized S and the lower poles are magnetized N, with a flow of current in one direction coil 27 will create an S pole to strengthen pole 23, while coil 28 will produce an N pole to weaken pole 24 and coil 29 will produce an N pole to aid pole 25, while coil 30 will produce an S pole to weaken pole 26 as indicated by the polar signs in this view. Under these conditions, a movement of the armature away from the" weaker .poles towards the stronger poles is produced, that is toward the left in the illustration and with a reversal of'burrent, the armature will be shifted toward the right.

The bifurcated pole pieces are shown in Fig. 1 as each made up of two long magnetic strips 38 held in their spaced relation by an intermediate magnetic strip 39 and the three strips held to the magnet yoke pieces 8 and 9 by embracing clamps 40 under the heads of the through bolts 10.

The pole pieces may be made up in laminated form as particularly shown in Figs. 5 and 6, where the polar laminations 41 are indicated clamped together between side plates 42 by through bolts 43 and where the supporting strips 33 are shown riveted at their upper and lower 'ends at 44 to wings or lugs 45 hint T is forms a solid unitary construction, which can be applied as such to the yoke of either an electro-magnet as in Fig. 1 or to the poles of an ordinary permanent magnet. These laminated polar units can thus be made up in stock and used with either the permanent magnets or electro-magnets as needed.

For a simplified form of the apparatus, the coils 27 28 and 29, 30 maybe used for field magnetizing as well as for armature actuating purposes, as indicated in Figs. 7 and 8 which show these coils energized in seriesparallel relation from a direct current source 46 and as being supplied through an audio frequency transformer 47 or the like with the so-called voice currents connected in bridge relation in between the olarizing coils at 48, 49, so as to superpose t ese alternating currents on the field magnetizing current, thus assisting and opposing the polar magnetization after the manner previously described, so as to efiect the lateral travel of the armature in the parallel sided magnetic gaps. The yoke structure for these pole pieces maybe like that shown in Fig. 1 with or without the magnetizing coil 11, or be in the form of a permanent magnet.

masses The armature, unburdened by windings or electric connections is suspended in a strong magnetic field acted on equally along its four corner edges by the two pairs of pole pieces, which it will be observed exert attraction across each side of the armature, between un like poles. Hence, the armature is balanced by these magnetic forces, aside from the supporting means, which latter serves more as a guide to prevent the armature from contacting the poles-and to cause it to travel parallel past the polar faces, after the manner of the armature in a rotating electric motor. Under these conditions of equal magnetic stress and freedom from external connections, the armature is highly sensitive to fluctuations and alternations in the actuating current and at the same time the action is powerful and positive. The driving unit as a whole is'of simple, sturdy construction and free of complicated or delicate parts, which might get out of order. The use of the coils for both field magnetizing and armature actuating purposes further simplifies and reduces the cost of the unit.

The armature is shown as of substantially rectangular cross section to provide corner edges substantially in alignment with the diagonally opposed corner edges of the magnet poles which are grouped in quadrangular relation about the armature. This armature as indicated, may be relatively long and the commonly employed in speaker units. The

sharply angled corners of the magnet poles and armature concentrate the flux at these points and the guiding and supporting means for the armature by confining the armature to a definite path enables the gaps at the corners of the armatures to be made as small as desirable. The movement of the armature is substantially transverse to its axis and at all times clear of the pole tips. Where the same coils are used for actuating the armature as well as energizing the field poles, the actuating current is connected as a bridging circuit, in between the two coils of each pair of pole tips, so that such current will have opposite eifects'on the two coils of each pair.

Because of the greater permissible straight line movement of the armature, the location of the controlling windings close to the pole ends and armature the long opposed pole the closed magnetic path for the variable flux across the armature and through the bifurcated pole'pieces, the action is particularly powerful, producing the desired bass tones even with a small size of diaphragm.

The simplified diagram, Fig. 8, shows possibly more clearly than Fig. '1 the actuating current from the transformer or other output as superimposed on the field coils in bridge relation, so that this actuating current traverses the coils without passing through the battery, leaving the battery current to traverse the coils without passing through the transformer, the two currents thus remaining in efiect independent, with the actuating current exerting the desired control elfect over the field polarizing-current. In practise, this control seems to be a maximum when the armature is equal in width to the space between adjoining poles so that proximate corners of the armature are immediately opposite proximate corners of adjacent poles.

What is claimed is:

1. In apparatus of the character disclosed, pole pieces magnetized to like polarity, oppositely magnetized pole pieces opposed in parallel closely spaced relation to the first pole pieces to form two aligned narrow magnetic gaps, a thin light non-polarized magnetic armature positioned to operate laterally in said gaps, a mechanical transmission connection engaged with said armature, means for guiding said armature for free movement in said gaps across the end faces of the opposing pole pieces with substantially constant clearance, operating coils on the pole pieces adjacent to the gaps for weakening the magnetic effect at one gap while simultaneously strengthening the magnetic eflect at the other gap, said armature being free from polarizing windings and by reason of for guiding said armature for free movement 7 in said gaps across the end faces of the opposing pole pieces with substantially constant clearance, operating coils on the pole pieces adjacent to the gaps for weakening the magnetic effect at one gap while simultaneously strengthening the magnetic efiect at the other gap, said armature being free from polarizing windings and by reason of its thinness forming short direct magnetic paths for the variable operating flux across the gaps between unlike pole pieces, said armature comprising an elongated thin bar of magnetic material and the pole pieces being correspondingly elongated in the direction of length of said bar, substantially at right angles to the direction of movement of the bar in the magnetic gaps. I

3. In apparatus of the character disclosed, pole pieces magnetized to like polarity, oppositely magnetized pole pieces opposed in par-v allel closely spaced relation to the firstpole pieces to form two aligned narrow magnetic gaps, a thin light non-polarized magnetic armature positioned to operate laterally in said gaps, a mechanical transmission connection engaged with said armature, means for guiding said armature for free movement in said gaps across the end faces of the opposing pole pieces with substantially constant clearance, operating coils on the pole pieces adjacent to the gaps for weakening the magnetic effect at one gap while simultaneously strengthening the magnetic effect at the other gap, said armature being free from polarizing windings and by reason of its thinness forming short direct magnetic paths for the variable operating flux across the gaps between unlike pole pieces, the guiding means comprising resilient spring strips secured to v the ends of the armature and extending'substantially at right angles to the length of the armature.

4. In apparatus of the character disclosed, a magnet yoke having bifurcated pole pieces projecting toward each other with their ends opposed in closely spaced parallel relation providing two short magnetic gaps, means for polarizing said bifurcated pole pieces, a

thin light, elongated magnetic armature structure supported for rectilinear bodily reciprocation in the two magnetic gaps in a plane substantially parallel with the end faces-of the bifurcated pole pieces, the ends '-'of the bifurcated pole pieces being correspondingly elongated in the direction of length of'the armature structure substan tially at right angles to the direction of movement of the armature structure, operating windings on the bifurcated pole pieces for strengthening the magnetic efiect across the armature structure at one of the aps while simultaneously weakening the e ect across the armature structure at the other gap, and a sound generating member having a mechanical connection with said armature structure.

5. The combination with a magnet yoke. of

a pole piece assembly for speaker units or the like, comprising bifurcated pole pieces and means securing the same together in opposed spaced relation for mounting as a unit on the ends of said magnet yoke, flexible strips at the opposite sides of said pole pieces and supported on said spacing means aforesaid, said spacing means having openings at opposite sides in line with the gaps between the bifurcated pole pieces, an armature bar 'fixed at its ends to said resilient supports and operating through said openings, in the 5 gaps aforesaid and operating windings on said bifurcated pole pieces.

In testimony whereof I aifix my signature.

, CLYDE J. FITCH. 

